Furnace Won’t Turn On | How To Troubleshoot A Not Working Furnace

A furnace is one of the principal components in our home. Needless to say, when a furnace stops working or is malfunctioning, you will notice right away (cold feet, anyone?). When this problem arises, the first impulse is to call in a repairman to fix whatever is wrong with your furnace.

But what if I tell you that you can save a few hundred dollars on professional help by fixing the problem yourself? Well, in this article, we’ll be tackling how to troubleshoot a furnace that won’t turn on.


The problem can be not as complicated as it seems. Sometimes, the fix is very simple and does not require a professional coming to your home, as in fixing a broken dryer. However, if you think that the problem is way beyond you repairman skills, consider calling in a pro to help you out. Nevertheless, here are the simple fixes that you can do when you find that your furnace is not working or is not kicking on:

How to Troubleshoot A Furnace That Won’t Turn On


Step 1: Check your thermostat

Sometimes, the problem is with your thermostat rather than the furnace itself. In any case, check your thermostat first.

  • First and foremost, check if the temperature is turned up high enough to warm up your home. Additionally, make sure that it is in heat mode and not air conditioning or cool.
  • Ensure that the date and time are correct, if you are using a programmable thermostat. A programmable thermostat is set to lower the temperature at specific times when it thinks nobody is home. Input the proper date and time then see if it fixes the problem
  • Check for a low battery indicator. A low or dead battery can mess up your thermostat’s settings, so make sure to replace your batteries from time to time. Pro tip: make certain that your batteries have enough juice, because a power interruption can reset the whole system and cause you more problems.
  • Check for loose or touching wires inside your device. Loose or jumbled wires may interfere with the thermostat’s system. In this case, they may need a little tightening and cleaning up.

If you’ve checked all the things in the list above and confirm that your thermostat is programmed and functioning properly, then we can move on to the next step:

Step 2: Check your wiring

If you don’t find anything wrong with your thermostat’s settings, then there could be something wrong with the connection between it and the furnace. This can most likely occur if you had any repair or remodeling done. What you need to do is:

  • Trace the wires leading to the furnace and check for any breaks. If you find any breaks, connect the wires back together and seal it with electrical tape.
  • This problem will most likely surface if you’ve done any wall repair/remodeling, so a personal tip is to know the location of your wires before doing any repair or remodeling, so you can take extra precaution not to damage them.
  • If you still feel the cold biting at you, your thermostat is more likely the problem. To verify this, locate the circuit board wherein your thermostat and furnace wires are connected, then cut the wires connected to the R and W terminals; connect a piece of jumper wire in between, and then see if your furnace works now.
  • If it does, then your thermostat is most likely defective. Remove the jumper wire and connect the R and W wires back together; you cannot use this as a temporary fix.

This goes to show that correct wiring is very important, as in wiring 3-way and 4-way switches.

On the other hand, if the furnace does not work with the jumper wire, move on to the next step.

Step 3: Check your furnace

At this point, we have confirmed that the thermostat is not the problem and we are moving on to simple furnace troubleshooting. Below are some troubleshooting tips for a furnace that won’t turn on/kick on:


Always remember to turn off your unit before attempting to fix/repair.


a. See if your air filter is dirty

Usually, this is the problem for furnaces that won’t turn on, and the solution is very simple. If your air filter is matted with dust, soot, and other particles, it will block the air returning to the furnace, thus, reducing the amount of hot air it can blow back out. 

This causes the heat exchanger to overheat because the furnace has to exert more effort into heating your home, and leads to your furnace turning off automatically.

So, what you need to do is simply turn off the furnace and change the air filter. See if this fixes the problem.Pro tip: change your air filters every 3-5 months to prevent problems.

b. Check if the furnace blew a fuse.

Locate your main electrical panels and subpanels that connect power to your furnace and see if the circuit has tripped. If it has, reset the circuit breaker. To do this, simply flip it off and then on again.

However, if you see any physical indications of burning or breakage on the fuse, replace it with another one of the same amp rating. If the circuit breaker trips again, there may be something wrong with your electrical wiring. In this case, call a professional. 

c. Make sure everything is in place.

If you’ve had any repairs done recently, your repairman may have forgotten to shut the blower motor panel properly. Locate your furnace blower motor panel and ensure that it is pressed all the way down. Underneath that panel is another switch, so make sure this is pressed firmly, too.

If your furnace is still not working, confirm that the gas valve is turned on as well. To do this, simply turn the handle such that it is perpendicular to the gas pipe.


Never replace a fuse with another one that has a different amp rating.

d. Clear the chimney exhaust flue.

Sometimes, your problem stems from animals making home in your chimney or your pipes icing over. If you suspect that this is the case (which can happen especially during the winter), check your chimney pipe from the top of the furnace for any blockage.

Moreover, check outside to make sure that nothing is blocking the end of the pipes as well.Another thing to note: you will also need to check the inducer fan if it is working. If not, call in a repairman.

e. Clean or replace the flame sensor.

If your furnace constantly goes out after you’ve repeatedly turned it on, you may want to consider cleaning and/or replacing the flame sensor.

f. Clean out drain lines.

Your drain lines can become obstructed by molds and residues, which causes automatic shut-down of your furnace. Locate your drain hose and see if this is the problem. If you find it dirty and/or obstructed, use a mixture of bleach and water to clean out the hose.

g. Make sure your air ducts are not the problem.

If hot air is not blowing in specific parts of the house, look for handles on the ducts as well as leaking ducts (with holes, gaps, breakage). Ensure that the handles are turned so that the ducts are fully open.

For the latter case, seal the leaking ducts with mastic sealant or metal duct tape.


These are the basic troubleshooting methods you can do on your own when you find your furnace not working or not kicking on. However, it is important to determine whether the problem is within your capacity as a DIY repairman.

I recommend calling a professional for more advanced repairs, as to not risk further damaging your furnace nor the safety of your home.


If your furnace problem entails a simple solution, this article will definitely help you out. Now that we’ve learned the basic troubleshooting methods a DIYer can certainly do on his own, you can now start looking for the problem and fixing it with the simple steps highlighted in the prior sections. Nevertheless, remember to take not of the safety precautions before anything else.

Did you find this article helpful? If you have any more questions regarding this topic, let me know in the comments below. Just as such, comments and suggestions are also appreciated. If you liked this article, don’t forget to share it with your friends. Thanks for reading!

VIDEO: Furnace Troubleshooting


  • Emma Clark

    Hi there! My name is Emma Clark, a part-time interior designer, house flipper, and full-time mom. This blog is the fruit of my extensive experiences as an interior designer and home improvement enthusiast. More so, I'm here to share with you a lot of great ideas on what you can do to make your home into a masterpiece: all cost-effective and amazingly creative.